A surprising number of us don't take medications as prescribed. We skip rehabilitative therapy. And forget about our doctors' admonitions to stop smoking, cut down on the beer, eat a healthy diet and get some daily exercise.

Depending on which health condition you're looking at, researchers say as many as half of patients ignore their doctors' instructions. And starting with today's Thanksgiving feasting, doctors know we're entering the annual holiday period of peak noncompliance. Take too much rich food, washed down with too much alcohol, and then don't take your medication, and you've got a potential prescription for the emergency room, especially if you have a chronic condition such as heart disease or diabetes.

Even after a life-altering experience like a heart attack, only half of patients took the prescribed medication, according to a recent study. This despite the fact that the drug was free and patients were told clearly that it was lifesaving, according to the report, released last week by the American Heart Association.

"In medical school they taught us the rule of thirds," said Narvarte, who summed it up like this: One third of patients will take their medication exactly as prescribed and do everything the doctor tells them to do all the time; another third will do their best and get it right most days. "And one third can't do it at all," said Narvarte.

Why are patients so resistant?

• Some can't afford the cost or the co-pays associated with medications and therapies. "I see patients in clinic at the end of the month who tell me they haven't taken their medication for a week because they ran out of money and are waiting for their next check to arrive to get their prescription filled," said Dr. Leslie Miller, chair of cardiovascular sciences at USF Health.

• Another common reason, especially around any holiday, is just being distracted. Whenever your normal daily routine changes, medication slip ups are more likely, particularly when you take several drugs multiple times throughout the day.

• People with so-called silent symptoms — such as high blood pressure and high cholesterol — may not to take their pills because they feel fine. "Those medications may not make you feel noticeably different, but they do an important job of preventing heart attacks and stroke," Miller said.

• Side effects can also be a deterrent. Narvarte has a hard time getting his patients to take cholesterol-lowering statins because they fear developing muscle aches — a potential, but not very common side effect. "It's a shame, because they can really benefit from being on a statin to reduce the risk of future cardiovascular events," he said.

Drowsiness, fatigue, lightheadedness, sexual dysfunction, and frequent urination are more side effects that inspire pill-skipping. "Patients will skip diuretics taken for blood pressure because they don't want to have to pull off the road or get up from the dinner table to go to the bathroom repeatedly," said Miller.

Of greater concern is the organ transplant patient who misses a dose of anti-rejection medication, the diabetic who misses a dose of insulin, the AIDS patient who misses an anti-viral drug.

But even less obviously critical conditions can make noncompliance dangerous. Suddenly stopping antianxiety medication can cause potentially fatal seizures. Stopping some hypertension drugs can cause a dangerous spike in blood pressure. Skip your antidepressant for a couple of days and Narvarte said, "You'll know it. You'll feel awful."

.FAST FACTS

The cost of noncompliance

The National Consumers League estimates that medication noncompliance results in:

• More than a third of medication-related hospitalizations.

• Up to 125,000 deaths.

•$290 billion a year in avoidable healthcare expenses.

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For tips on how to stay on track with your medications visit www.scriptyourfuture.org.